Step 23
Add a new layer and name it 'skirt'.

 

Step 24
Grab your 'freehand' selection tool             and set the tool options to match the image below.

Starting where the arrow indicates,  click an outline of a skirt.  You want to come out of the 'back' image at the bottom of the sleeve and fan the skirt around the seat so that the entire seat is enclosed in the selection.   When you have made the selection up to the low end of the sleeve on the opposite side, double click to set the selection.  Try NOT to have the high points of the selection at the exact same height;  let one side be  a little lower than the other for the sake of realism.

Set the background/fill color to the pattern you are using for the skirt.

In the Layers palette, the 'skirt' layer is active;  drag it down and drop it between the 'seatrim' layer and 'Layer1'.
        
Your image should look something like this.

Apply the 'cutout' filter using the same settings as in the image below.
                                 
 

Step 25
Switch to the 'freehand' selection tool and click some slight waves into the hemline.

 

Step 26
Switch to the paintbrush, using the settings below

Make strokes, starting in the seat area and stroke downward to simulate folds.

Switch to the  'retouch' tool using the settings below

Follow the same strokes one time each to blur the folds lightly.